The present invention relates to a substrate processing apparatus used in the fabrication process of semiconductor devices, LCDs, or the like, and comprising a process solution supply system for supplying a process solution, such as a developing solution.
In the photolithography step included in the fabrication process of a semiconductor device, a resist solution is coated on a substrate, such as a wafer, to form a resist film. The resist film is exposed to light, with a predetermined pattern used as a mask, and is then subjected to developing treatment, thereby forming the predetermined pattern on the resist film.
These series of process are carried out by a coating-developing system.
In this coating-developing system, process solutions, such as a developing solution and thinner, are supplied to various types of process units provided for the coating-developing system, namely, an adhesion unit, a resist coating unit, a developing unit, etc. The process solutions are first forcibly supplied to an intermediate tank by an N.sub.2 gas-based forcible supply apparatus. After being stored in the intermediate tank, the process solutions are supplied to the process units. As a means for supplying the solutions from the intermediate tank, either a pump or an N.sub.2 gas-based forcible supply apparatus is employed.
In the case where the pump is used for supplying the process solutions from the intermediate tank to the process units, the process solutions are repeatedly compressed. It is therefore likely that the process solutions are in pulsatory motion when they reach the process units. For this reason, in many cases, the N.sub.2 gas-based forcible supply apparatus is employed as the means for supplying solutions from the intermediate tank to the process units. In the case where the N.sub.2 gas-based forcible supply apparatus is employed, a compressed N.sub.2 gas is blown directly into the process solution stored in the intermediate tank, and the process solution compressed thereby is supplied from the intermediate tank to the process units.
However, when the N.sub.2 gas-based forcible supply apparatus is employed, the compressed N.sub.2 gas is blown directly against the process solution. As a result, the process solution contains the N.sub.2 gas. When the process solution reaches the process units and its pressure decreases, the N.sub.2 gas in the process solution may turn into bubbles. If the process unit is, for example, a developing unit, the bubbles of the N.sub.2 gas may be included in the developing solution. If this happens, the process may be adversely affected, and uniform development cannot be expected.
In addition, the electronic flowmeters employed in the coating-developing system include a type which cannot make accurate measurement if such bubbles are included. This means that the process solution may not be supplied in an accurate amount.